Once you've received the key, you can use it to open the door and gain access to the rest of the dungeon, which is fairly extensive and filled with quite a few puzzles. The solution for the dragon claw door (from top down) is moth, owl, wolf.

As you proceed through the dungeon you'll eventually find yourself at the bottom of a winding stairwell. There is a trapdoor here into the water. There is some loot in the water, and a chain on the opposite wall that will close the trap.

If you head all the way to the top of the stairs you'll find a locked door (master). Behind it is a locked chest (expert) with some of the best loot you're going to find in this dungeon. Take it or leave it then head halfway back down the stairs and open the door. Pause for a minute until the booby trap arrows stop flying, and head through.

At the bottom of the short stairs is a pressure plate with another booby trap. Head down the next set of stairs and you find yourself in a room with some raised bridges, and a treasure room that you can see through a hole in a closed door. To get into the treasure room you'll need to find and activate two handles. The first is to the left of the door you just came through (next to a coffin in the wall). The second is around the corner to the right next to a coffin.

Grab what you want from the treasure room then head out and clear the skeletons out of the room below you. This can easily be done from above with magic or archery, or you can do it the fun way - directly above the pool is a chandelier with two pots hanging from it. You can throw flames at the pots (or possibly use archery?) to drop them into the pool below, setting the pool on fire and presumably doing away with the skeletons.

It is unclear if there is a way to lower these bridges, or what the value of lowering them might be.

Head down the stairs, then back up the opposite set of stairs, through the iron door and continue on. Eventually you will come down into a waterway, with water rushing into a closed iron gate. There is a pull chain to the right of the gate. Under the water is a skeleton and a coin purse. If you follow the waterway upstream it leads to a waterfall, which you can walk into for some not too exciting loot.

Head up the log stairs into a room with a raised bridge, a pressure plate, and four 3 sided pillars with animal insignias on each side, which can be turned by activating them. To find the correct pillar alignments, head into the next room and step on the pressure plate you find there. Stay on it long enough for the stone doors to rotate open and reveal the answers. Once you've have the correct animals on each pillar, step on the pressure plate to lower the bridge.

Across that the bridge there is a locked iron door on the right. Inside you'll find a gold ingot. If you take the ingot be warned that it is sitting on a pressure plate that activates a stream of fire.

Continue down through the door into Shroud Hearth Depths, and be prepared for a slew of draugrs. Clear the room then head into the next where you'll find a chest with some significant weapons and loot.

In the next room, pull the chain to the right of the stone door, head down the passageway and pull another chain to get through another stone door. You'll eventually find yourself back in the room where you found the journal.